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Literature Review Additive Manufacturing Engineering Essay

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For fast changing needs of industry, adoption of alternative process capable of fulfilling the needs was necessary. This need pushed the development of new technologies over the period. Some of these technologies together under an umbrella are called Additive Manufacturing (AM). This approach eliminated tooling costs, reduced lead time and offered design freedom for producing products (Hopkinson, Hague et al. 2006).

Additive Manufacturing produces parts from data obtained from 3D models, CT scans, MRI and reverse engineering. This data is fed into commercial machine software. thus producing parts from the machine. This means with AM processes, the products are directly made from CAD. The numbers of application are increasing as the process is being developed and improved. Processes like Stereolithography, Laser Sintering, Fused Deposition Modelling, 3D Printing, Ultrasonic Consolidation (UC), etc. are used for AM most widely

With adopting AM processes, the product development and manufacturing has been revolutionised. This has also enabled users to get What You See Is What You Get (WYSIWYG)(Gibson, Rosen et al. 2010)

AM enabales to to built parts in single piece in contrast to traditional manufacturing processes. Due to limitation of processing the parts were built separately and assembled. Manufacturing single part helped reduce the cost and weight of part. Figure shows a part built for automotive industry. There was in total___ reduction of weight due to AM.

With recent developments in AM, it is now capable of manufacturing micro-level parts. Parts earlier impossible to make, AM makes it possible to produce the assembly as single part. Cohen et. al. (2010) (Cohen, Chen et al. 2010), built fully functional parts with Ni-Co alloy with Electrochemical fabrication process (EFAB® )process. It has been suggested in the study, this will find commercial application in medical industry, electronic components, microfludic devices and other devices from millimetre to centimetre sizes. Figure 2 shows a folded and unfolded millimetre-wave hybrid coupler produced by EFAB®.

Figure 2 Folded and Unfolded millimetre-wave hybrid coupler produced using EFAB (Cohen, Chen et al. 2010).

Overview of Additive Manufacturing technologies

Metals Processes

Powder Bed Deposition

Selective Laser Melting (SLM)

Direct Metal Laser Sintering (DMLS)

LaserCusing

Indirect Selective Laser Sintering (SLS)

3D Printing (3DP)

Electron Beam Melting (EBM)

Powder Feed Deposition

Laser Engineered Net Shaping

(LENS)

Direct Light Fabrication (DLF)

Direct Metal Deposition (DMD)

Laser Consolidation (LC)

Other Processes

Ultrasonic Consolidation (UC)

Maskless Mesoscale Material

Deposition (M3D)

Shape Deposition Manufacturing

(SDM)

Cold Gas Dynamic Manufacturing (CGDM)

Layered Object Manufacturing (LOM)

Electrochemical Fabrication Process (EFAB)

Deposit Laser Welding (DLW)

Ceramic Processes

Selective Laser Sintering (SLS)

Selective Laser Melting (SLM)

Fused Deposition of Ceramics (FDC)

3D Printing (3DP)

Additive ManufacturingAdditive Manufacturing is a group of layer-by-layer technologies. These technologies are capable of using polymers, metals and ceramics. The material used in production could be in form of wire, liquid or powder. Figure 2 shows different types of AM Processes.

Polymer Processes

Selective Laser Melting (SLM)

Selective Laser Sintering (SLS)

High Speed Sintering (HSS)

Fused Deposition Modelling (FDM)

3D Printing (3DP)

Selective Mask Sintering (SMS)

Direct Light Processing (DLP)

Figure 2 Additive Manufacturing Technologies (Mumtaz, Loughborough University. 2008)

AM technologies can be further classified based on medium used to consolidate the material as laser and non-laser technologies. Figure 2 classified the metal AM technologies further by the method of material deposited on the build tray/ platform. Powder based AM technologies can be classified into powder bed deposition and feed deposition.

Powder Bed Deposition

Figure 2 shows a powder bed deposition schematic diagram. The powder from the delivery system is spread on the preheated substrate at start or on the consolidated layer. The powder spread by the hopper is levelled to the defined layer thickness in the program. Consolidation of the layer is carried by laser for SLM, SLS, and DMLS systems and by other medium for respective technologies. On completion of consolidation of the layer material, the platform moves vertically down by a step of single layer thickness.

Figure 2 Schematic of Powder Bed Deposition (Mumtaz, Loughborough University. Wolfson School of Mechanical and Manufacturing Engineering 2008)

This system is used in different type of technologies. Technologies like SLM, DMLF, LS, 3DP etc use powder bed deposition system. The layer thickness is in the range of 20µm to 100µm (Hopkinson, Hague et al. 2006)(Levy, Schindel et al. 2003)(Schueren, Kruth 1995). The unmelted/ un-sintered powder in this system is blended with virgin powder and reused.

The thickness of the layer is a parameter in the process to control. The parts produced by Layer Manufacturing (LM) have an issue of rough surface finish. In several studies, it has been reported the need to select optimum layer thickness as the degree of sintering, surface roughness and mechanical properties are highly affected.

Powder Feed Deposition

Figure 2 shows a schematic of powder feed deposition system. The laser is used to create a melt pool. The powder is injected from the sides to the melt pool. An inert gas shield is envelopes the melt to prevent from oxidation (Kreutz, Backes et al. 1995) (Vilar 1999) (Santos, Shiomi et al. 2006) (Laeng, Stewart et al. 2000). As the interaction zone moves along the part surface, the molten material starts to solidify and forms track of homogeneously melted material. Two adjacent tracks have a partial overlap in order to produce continuous layer of the material (Costa, Vilar 2009). The flow and angle of powder feed is critical for a good seam. The melting and

Figure 2 Schematic of Powder Feed Deposition

Several laser system uses powder feed. The geometry control from powder feed is better compared to wire feed (Waheed et al 2005). The major drawback of this method is that wastage of the expensive powder is very high; the powder is delivered at such a speed that it bounces off the target surface and also the powder feed stream size is larger than the laser beam spot size on the target (powder around the edge is not fused and is wasted). (REF). Several technologies have developed incorporating the powder feed deposition for additive manufacturing. Table ... shows processes using powder feed for AM.

TABLE FROM Laser powder deposition.pdf

Powder Bed Technologies (classification, SLS no support as supercooling of polymer)

With Additive Manufacturing gaining acceptance in manufacturing from prototyping, powder bed technologies have played a key role. Laser and powder bed based technologies holds a unique position in the transition. These technologies allow processing of polymers, metals, ceramics and several composites (Kruth, Levy et al. 2007). In order to process these materials several mechanisms have been used.

According to Kruth et al. (Kruth, Froyen et al. 2004), these mechanisms are solid-state sintering, chemically induced binding, liquid-phase sintering or partial melting, and full melting. Solid-state sintering, chemically induced binding, and liquid-phase sintering generally produce "green" parts (partially dense items made of either polymer-bonded powders or sintered-type powders) that require some post-SFF treatment to achieve full density and improve strength, hardness, machinability and thermal conductivity. The post- SFF treatment may consist of debinding of polymer binders, furnace post-sintering, hot iso-static pressing or an infiltration with a convenient low melting point material. SLS with partial melting of the feedstock powders can produce functional fully dense metal parts (Santos, Shiomi et al. 2006)

SLM

Selective Laser Melting (SLM) is capable of producing complex 3D parts from direct metal powder by way of melting layer by layer. SLM parts requires minimum or no post processing such as furnace densification cycles or infiltration of secondary materials (Gu, Shen 2007). However, processing like surface preparation is done when required.

The development of SLM is not to par with SLS. There are several reasons to this. However priory it was high laser output and lack of precise control of the melting atmosphere were of concerns. However, initially to start using metals in laser sintering this was overcome by using high and low melting point materials (Manriquez-Frayre, Bourell ).

SLM is capable of producing intricate parts that are not possible from traditional manufacturing.

Polymer and indirect metal technologies are widely used in direct manufacturing. However direct metal technologies are subjects of current research.

At present SLM is capable of using different powder systems. These systems can be classified into single component powder, pre-alloyed powder and multi-component powder systems.

Process

Parameters

Part features

Physical and Mechanical

Applications of SLM

Issues (highlighting disadvantages of supports)

Supports are required to

anchor down certain unsupported features due to shrinkage and curling of solidifying

19

material. This restricts the processes' geometric freedom and incurs further post

processing operations to remove supports.

Anchorless SLM

Materials

Classification (melting point, metals/non metals and others)

Powder Mixing

Mixing Methods

Eutectic Materials (for ASLM)

Research Scope

Definition

Novelty

Objectives

Initial results

Investigating candidate alloys for this research.

Project Plan

Conclusion

References


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